fellyoudaoicibaDictYouDict[fell 词源字典]
fell: English has no fewer than four separate words fell, not counting the past tense of fall. Fell ‘cut down’ [OE] originated as the ‘causative’ version of fall – that is to say, it means literally ‘cause to fall’. It comes ultimately from prehistoric Germanic *falljan, causative of *fallan ‘fall’. Fell ‘animal’s skin’ [OE] goes back via Germanic *fellam (source also of English film) to Indo-European *pello- (whence Latin pellis ‘skin’, from which English gets pellagra [19], pellicle [16], and pelt ‘skin’ [15]). Fell ‘hill’ [13] was borrowed from Old Norse fjall ‘hill’; this seems to be related to German fels ‘rock’, whose ultimate ancestor was Indo-European *pels-.

And the adjective fell ‘fierce, lethal’ [13] was borrowed from Old French fel, ancestor of English felon.
=> fall; film, pelt; felon[fell etymology, fell origin, 英语词源]
fell (v.1)youdaoicibaDictYouDict
Old English fællan (Mercian), fyllan (West Saxon) "make fall, cause to fall," also "strike down, demolish, kill," from Proto-Germanic *falljan "strike down, cause to fall" (cognates: Old Frisian falla, Old Saxon fellian, Dutch fellen, Old High German fellen, German fällen, Old Norse fella, Danish fælde), causative of *fallan (source of Old English feallan; see fall (v.)), showing i-mutation. Related: Felled; feller; felling.
fell (adj.)youdaoicibaDictYouDict
"cruel," late 13c., possibly late Old English, perhaps from Old French fel "cruel, fierce, vicious," from Medieval Latin fello "villain" (see felon). Phrase at one fell swoop is from "Macbeth." Related: Fellness.
fell (n.1)youdaoicibaDictYouDict
"rocky hill," c. 1300, from Old Norse fiall "mountain," from Proto-Germanic *felzam- "rock" (cognates: Old High German felisa, German Fels "stone, rock"), from PIE root *pel(i)s- "rock, cliff." Old High German felisa "a rock" is the source of French falaise (formerly falize) "cliff." Now mostly in place-names, such as Scafell Pike, highest mountain in England.
fell (v.2)youdaoicibaDictYouDict
past tense of fall (v.), Old English feoll.
fell (n.2)youdaoicibaDictYouDict
"skin or hide of an animal," Old English fel "skin, hide, garment of skin," from Proto-Germanic *felnam- (cognates: Old Frisian fel, Old Saxon fel, Dutch vel, Old High German fel, German fell, Old Norse fiall, Gothic fill "skin, hide"), from PIE *pel-no-, suffixed form of root *pel- (4) "skin, hide" (see film (n.)). Related: Fellmonger.